The invention deals generally with underground structures such as manholes, utility vaults, and pump stations, and more specifically with a method and apparatus to attach an impermeable continuous liner to prevent corrosion by the effects of sewer gas and to prevent fluid leaking into the underground structure.
Underground structures such as manholes serve to connect pipes, transfer sewage, and provide maintenance access. When they permit ground water to leak in, they contribute to unnecessary sewage treatment costs or damage the sewer lines or other utility services which pass through the underground structures. Furthermore, microorganisms that consume sewer gas form sulfuric acid, and this acid dissolves the underground structure walls which may lead to deterioration, collapse, service interruption, or accidents.
This deterioration is caused mainly because of the nature of the original structure. Underground structures such as manholes are essentially chambers in the ground, sometimes large vertical shafts, which extend to the depth at which sewer pipes or utility services are located. The older chambers are usually built of bricks or cement blocks, with the bricks or blocks assembled with mortar joints. These materials, and particularly the joints, deteriorate with time because of such factors as traffic loads, ground water, soil pressure, and septic gases. Even cast concrete underground structures can be damaged by such causes, particularly from the acids septic gases create and which attack most materials.
Once an underground structure is damaged and leaking, it is very difficult to repair it so that it is watertight and gas tight, and completely rebuilding it is costly and time consuming because it requires excavating all around the underground structure.
Several patents have been issued on a newer approach to repairing underground structure chambers. The technique involves attaching a liner to the inside wall surface of the underground structure chamber. As described in U.S. Pat. Nos. 5,490,744 and 5,265,981 by McNeil, the liner is typically a long fiberglass bag covered with an epoxy resin. This bag is lowered into the underground chamber, inflated by the use of a removable interior inflatable bladder until it presses against the inside walls of the underground chamber, and the resin is cured in place. The result is the formation of a new chamber which conforms to the original underground structure regardless of whether the chamber is a straight cylinder or it has an irregular shape. However, this type of additional internal chamber still has problems.
The structure of the McNeil liners, which have fiberglass and resins on the exposed surfaces, are themselves attacked by septic gases. This causes erosion of the exposed fiberglass layers which deteriorate over time and ultimately weaken the rehabilitation structure. Furthermore, at liner termination points such as junctions where the liner is joined to pipes and flow channels, gas infiltration leads to corrosion of the underground structure walls and destruction of the liner bond.
It would be very beneficial to have a underground structure liner which was chemically stable, allows gas-tight joints with pipe lining, and prevents fluid leakage into the underground chamber.
The present invention solves the problems with crumbling of fiberglass epoxy layers that are exposed to sewer gas and of joint adhesion with pipe linings by constructing the liner in a different fashion. The liner of the present invention includes two essential layers. The first layer is an acid resistant layer which is the innermost layer, the layer exposed to the environment of the underground structure. The second layer is located on the outside and is the layer in contact with the wall of the underground structure. This layer is a fleece layer, a continuous layer of fibers protruding from the acid resistant layer. The fleece layer is integrated into the acid resistant material and serves to capture and retain the epoxy resin applied to the liner. Furthermore, the fibers of the fleece layer function as multiple anchors as they contact the wall of the underground structure and form a continuous layer which conforms to irregularities and crevices in the underground structure wall surface. Reinforcing material can also be added to the fleece layer. Typically this reinforcing material is a cloth layer which is also saturated with resin, and it can be added to the outside of the fleece layer. However, the reinforcing material can also be integrated into the epoxy resin by applying a mixture of epoxy resin and fibers directly onto the fleece layer.
In the preferred embodiment the material of the acid resistant layer is polyvinyl chloride (PVC), the fleece layer is polyester, and the cloth layer is fiberglass. The thicknesses of the layers can be adjusted for the specific application to yield, for instance, greater strength or acid resistance.
Several methods of applying the epoxy resin are available. A two part resin can be applied to the fleece layer or to the fiberglass layer at the installation site just before insertion into the underground structure. A delayed reaction epoxy can also be applied to the liner before it arrives at the installation site, in which case the epoxy is cured by subjecting the assembly to elevated temperature or to some other activating agent such as light or other radiation.
The present invention also affords a means to create a superior seal between the liner installed within the underground structure and the pipes entering into the underground structure. To accomplish this, a PVC cap is formed which is inserted into the end of the pipe at the underground structure. This cap is held in the pipe with an expansion ring, and the cap extends out of the pipe end and is bonded to the liner and to a fiberglass disc which is attached to the bottom of the underground structure.
The liner of the present invention and the pipe seal together completely protect the original underground structure walls from any further contact with acid products from within the underground structure while also strengthening the walls and preventing ground water from leaking into the underground structure.